Listen to Robert Emmerich introduce The Big Apple, a hit song from 1937. Music written by Bob and performed by Tommy Dorsey's Clambake Seven with Bob on piano. Lyrics written by Buddy Bernier and sung by Edythe Wright. Audio provided by Dorothy Emmerich.

An athletic supporter is also a jockstrap. The line actually had been used in the 1950s. “Back the football team. If you can’t be an athlete at least you can be an athletic supporter,” an Iowa newspaper printed in 1955.

Wikipedia: Athletic supporter
An athletic supporter is an individual who spends time with athletes at the Collegiate and Professional level, but are not athletes themselves. The term often used pejoratively by families of athletes describing the “groupies” that often are around athletes.

Athletic supporter may also refer to:

. Jockstrap, men’s undergarment designed for use in sports
. Booster club, contributes money to an associated club, sports team, or organization

15 September 1955, Ida County Pioneer Record (Ida Grove, IA), “Hogan’s Alley,” pg. 9, col. 3:
Back the football team. If you can’t be an athlete at least you can be an athletic supporter.

Google BooksEve Arden: A Chronicle of All Film,
Television, Radio and Stage Performances
By David C. Tucker
Jefferson, NC: McFarland & Company, Inc.
2012
Pg. 133:
In another of her well-remembered lines from the film, she urges the student body to lend their support to Rydell’s sports program, saying, “If you can’t be an athlete, be an athletic supporter!”

Google BooksOnce Apun A Time:
A Rich, Historical and Sometimes Earthy Collection of Puns
By Robin Leech
Victoria, BC: FriesenPress
2015
Pg. ?:
If you cannot be an athlete, at least be an athletic supporter.

Twitter
NOLA guy
‏@NOLAguys
@Laura_Buchtel @carl_arredondo @zephyrsbaseball As they said in Grease, “If you can’t be an athlete, be an athletic supporter!”
5:26 PM - 19 Apr 2016